May 12, 2010 -- Bleary-eyed shift workers appear to make fewer mistakes on the job when they consume caffeine, such as a cup of coffee or a caffeinated energy drink, researchers report.

Shift and nighttime work can sometimes disrupt the body's natural clock, or circadian rhythm. This can lead to shift-work disorder, a sleep disorder in which a person has symptoms of insomnia or excessive sleepiness related to work schedules. The lack of quality sleep can make workers very drowsy while at work.

About 14% of Americans are shift workers, according to the National Sleep Foundation. Nurses, truck drivers, and emergency personnel are some examples of people who usually work off-hour shifts. Sleepiness on the job has been linked to medical errors, automobile accidents, and occupational injuries.

Researcher Katherine Ker and colleagues of the London School of Hygiene & Tropical Medicine reviewed data from 13 studies regarding the effects of caffeine on shift workers' performance. Participants were between the ages of 18 and 65, but most were between the ages of 20 and 30.

Depending on the study design, the workers received caffeine through coffee, energy drinks, food, or pills. In most studies, the workers completed neuropsychological tests to gauge their memory, attention, reasoning, and perception skills. Several studies compared the results of neuropsychological testing in participants given caffeine versus a placebo.